https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97679
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Patrick Palka <ppa...@gcc.gnu.org>: https://gcc.gnu.org/g:05708d6eef87a3dd0c68b1aed7f8d9c3824062b8 commit r11-8064-g05708d6eef87a3dd0c68b1aed7f8d9c3824062b8 Author: Patrick Palka <ppa...@redhat.com> Date: Thu Apr 8 13:07:37 2021 -0400 c++: constrained CTAD for nested class template [PR97679] In the testcase below, we're crashing during constraint checking of the implicitly generated deduction guides for the nested class template A::B because we never substitute the outer template arguments (for A) into the constraint, neither ahead of time nor as part of satisfaction. Ideally we'd like to avoid substituting into a constraint ahead of time, but the "flattening" vector 'tsubst_args' is constructed under the assumption that all outer template arguments are already substituted in, and eliminating this assumption to yield a flattening vector that includes outer (generic) template arguments suitable for substituting into the constraint would be tricky and error-prone. So this patch takes the approximate approach of substituting the outer arguments into the constraint ahead of time, so that the subsequent substitution of 'tsubst_args' is coherent and so later satisfaction just works. gcc/cp/ChangeLog: PR c++/97679 * pt.c (build_deduction_guide): Document OUTER_ARGS. Substitute them into the propagated constraints. gcc/testsuite/ChangeLog: PR c++/97679 * g++.dg/cpp2a/concepts-ctad3.C: New test.
